A hard disc drive (HDD) has been widely used as an information storage medium. However, recording density of a hard disc drive is increasing more and more, closing to super paramagnetic limit where magnetic information becomes instable.
The super paramagnetic limit is explained below with reference to equation (1).−kmV/kT  (1)
Equation (1) indicates thermal fluctuation constant, and km, V, k, and T indicate magnetic anisotropic energy, recording bit volume, Boltzmann constant, and absolute temperature, respectively. In a conventional medium for magnetic storage (hard disc), volume (V) of recording bit decreases as recording density becomes higher, and consequently the thermal fluctuation constant becomes larger. It is generally known that larger thermal fluctuation constant results in instability of magnetic information, such as accidental spin inversion.
Therefore, in order to realize higher density, there has been studied hybrid storage that is generally called heat-assisted magnetic recording, optical-assisted magnetic recording, laser-assisted magnetic recording etc. In the hybrid storage, a magnetic storage layer having high capacity of magnetic information at room temperature is used in a storage medium in order to prevent instability of magnetic information, and at the time of magnetic storage, an external magnetic field is applied while the temperature of a magnetic storage area is increased in order to facilitate spin inversion.
This allows forming a magnetic storage bit smaller than external magnetic distribution in a case where heat gradient steeper than external magnetic gradient is given to the surrounding of the magnetic storage area.
In order to heat such magnetic storage layer, evanescent light that is localized sufficiently smaller than diffraction limit of light is employed. Evanescent light is generated by irradiating laser to an evanescent light generation mechanism made of a minute metal opening smaller than the wavelength.
Patent Document 1 discloses a recording/reproduction head 100 that is a slider in which a semiconductor laser 102, a ¼ wavelength plate 134, a transparent light-converging medium 106 serving as an evanescent light generation mechanism, an optical spot 109a, and an optical system are integrated, as illustrated in FIG. 15.
With the configuration, linearly polarized light generated from the semiconductor laser 102 is converted by the ¼ wavelength plate 134 into circularly polarized light and then passes through the transparent light-converging medium 106 so as to be converged to the optical spot 109a. Light emitted from the optical spot 109a is evanescent light 109b. Converting the linearly polarized light into the circularly polarized light allows forming thermal distribution that is rotation-symmetrical with respect to a magnetic storage layer (not shown).
However, a slider used in a hard disc drive is getting smaller year after year. The size of a general slider at present is approximately 0.8 (depth)×0.7 (width)×0.3 (height) mm. The weight of a general slider is decreasing exponentially as the slider is getting smaller year after year. It is expected that the weight will decrease further.
It is known that, in general, as the size of a slider gets smaller and the weight of the slider decreases, moment of inertia of a suspension to which the slider is fixed drops, making the access speed higher.
On the other hand, the length of a resonator of edge-emitting semiconductor laser ranges from 0.2 to 1.0 mm, the width of a chip ranges from 0.2 to 0.5 mm, and the height of the chip ranges from 0.1 to 0.3 mm, which is substantially the same size as the aforementioned small slider. That is, the integrated slider with the above configuration where the optical lens and the wavelength plate are combined has a problem that it is difficult to downsize the slider and that there is a possibility that the slider gets larger.
[Patent Document 1]
Japanese Unexamined Patent Publication No. Tokukai 2004-362771 (published on Dec. 24, 2004)
[Non-Patent Document 1]
W. L. Barnes, A Dereux, T. W. Ebbesen, Nature 424, 824 (2003)